What is a Site Investigation in Civil Engineering?

In order to properly plan and execute a project, an engineer must be well-informed about the surroundings of the job site. Understanding the physical characteristics and existing layout of soil materials is critical to successfully break ground on a new development. Often referred to as soil exploration, site investigation relies on a variety of field and lab tests to determine the best course of action for any given build. So, what is site investigation in civil engineering? Learn more about site investigation techniques in construction, and the reasons for site investigation below.

Why is Site Investigation Necessary?

One might assume that an experienced engineer may be able to tackle any project on expertise alone. However, each job offers unique challenges and opportunities that present many reasons for site investigations to be conducted. A good design for any project must be financially prudent, physically safe, sound, and sometimes flexible. In order to hit the mark on all of these aspects, planning must start from below the ground on up. The reason for a site investigation is to understand the following:

  • The composition of soil layers and bedrock
  • Groundwater conditions
  • Durability, compressibility, and strength of soil, rocks, soil strata
  • Chemical composition of groundwater on site
  • Composition of foundations on nearby sites

soil samples

Soil Samples

What are the Stages of Site Investigation?

For most projects, the stages of a site investigation can be broken down into phases. The stages of site investigation usually coincide with the overall project planning. Site investigations will take place during the feasibility and planning stage, pre-construction, and construction phases when needed. So, what are the stages of site investigation? The three stages of site investigation are:

  1. Preliminary investigation
  2. Detailed investigation
  3. Supplementary investigation and construction recommendations

Let’s further explore the site investigation techniques for construction deployed, and what is site investigation in civil engineering at each stage below.

Site Investigation Stage 1: Preliminary Investigation

What are the stages of site investigation? The place to start is with heavy fact-finding during the preliminary investigation. You will want to gain a firm grasp of the type of structure being planned, the future use of the structure, and local building codes. At this point, the geotechnical engineer on the project can take certain actions to save time and resources. A thorough review of existing data can help cut down on the need for extensive original research. Geological data can be found through a number of sources including:

  • Survey maps
  • County soil maps from the USDA
  • USDOT soil manuals
  • Well logs
  • Other existing reports or permitting documents

Site Investigation Stage 2: Detailed Investigation

At this phase, samples will need to be taken from the intended site. A critical technique used in site investigation for construction involves creating test borings to sample disturbed and undisturbed soil. Samples may need to be collected from various depths for testing and observation. Depending on the project, one rule of thumb to start is to drill one exploration in each corner of the intended structure and in the center. Depending on the uniformity of the results, more borings may be added and further tests conducted. The borings should be at a minimum, deep enough to acquire samples past the unsuitable topsoil into firmer layers, extending to depths that accommodate the structure and design intent, including anticipated building loads.

Site Investigation Stage 3: Supplementary Investigation & Construction Recommendations

The final phase involves analysis and planning based on the results of the previous phases. The results of the rock, soil, and water samples will be used to determine the potential for risks. If the chemical composition of the groundwater is found to have any deteriorating effects, this phase allows for planning to combat the issue. Additionally, planning for potential earthquakes, groundswells, floods, shrinkage, permafrost, or erosion will be conducted at this step.

Work With Our Expert Team

If you are looking for leading expertise, turn to Central Geotechnical Services, LLC for guidance. Our firm has global experience and can provide you with answers and insight into your queries. If you have lingering questions about site investigation techniques used in construction or the process as a whole, get in touch to have a conversation about your upcoming project!